As mobile data service volume continues to grow, spectrum resources have become more and more scarce, and for network deployment and service transmission, it is impossible to meet the requirements of the increased data service volume by merely using licensed spectrum resources. Hence, for a Long Term Evolution (LTE) system, the network development and the service transmission on unlicensed spectrum resources may be taken into consideration so as to improve the user experience and expand a network coverage, and this LTE system may be called as Unlicensed LTE (U-LTE or LTE-U for short).
For the unlicensed spectrum resources, no specific application system has been planned, and they may be shared by various radio communication systems, such as Bluetooth and Wireless Fidelity (WiFi). The shared unlicensed spectrum resources may be used by various systems through resource preemption. For example, the WiFi system may preempt the resources on the unlicensed frequency band in the following ways. At first, it may monitor a channel, and in the case that an idle time of the channel reaches a Distributed Inter-Frame Space (DIFS), it may determine that the current channel is a clear channel. Then, sites which are waiting for access to the channel may be in a random backoff stage, so as to prevent the collision of the sites on the same resource. In addition, in order to ensure fairness, it is further speculated that the spectrum resource cannot be occupied by each site for a long time period. As a certain time period expires or a data transmission volume reaches an upper limit, the resource needs to be released, so that the other device or system can preempt the resource.
In the case that the LTE system operates on a carrier of the unlicensed frequency band, an LTE base station and a User Equipment (UE) also need to perform resource contention, so as to ensure that the spectrum resources can be shared fairly between the LTE system and any other device or system.
Currently, there is no concrete scheme about how the LTE system can operate on the unlicensed frequency band. One agreed method is to use the spectrum resources on a carrier of the unlicensed frequency band through a carrier aggregation (CA) mechanism, i.e., the carrier of the unlicensed frequency band may serve as a secondary carrier (Scell) in the CA mechanism for the data transmission.
In accordance with the provisions on the CA mechanism in a conventional protocol, it is impossible to meet the requirements in the case that the carrier of the unlicensed frequency band is applied to the CA.